The present invention relates to the processing of air contaminated by particulates entrained with the air during industrial operations.
Industries such as foundries and fabrication or welding plants use machinery which produces airborne particulates as a result of grinding, melting, forging, pouring, welding, shakeout, abrasive blast cleaning or other operations. Since the contaminated air may interfere with the operation of machinery and pose a definite health hazard to the workers, these machines are usually equipped with hoods or cabinets to confine the air which carries the particulates. The hoods and cabinets are connected to duct work and blowers which remove the air from the work area and ventilate it to the outside atmosphere. This, however, creates another health hazard since the particulates in the air discharged from such industrial operations may pollute the atmosphere. It is, therefore, common practice to treat the contaminated air for the removal of entrained particulates, as by means of a dust collector, electrical precipitator, water wash or the like. Such systems for treating exhaust air or gases are efficient from the standpoint of removal of the larger particulates but are less efficient in the removal of dusts and fine particulates. These finer particles pose a health hazard and the O.S.H.A. PEL (Permissible Exposure Levels) generally prohibit recycle of such treated air to the workers' general breathing zone. Hence, even the filtered or treated air must be discharged to the outside atmosphere.
Removing the air from the workers' breathing zone, filtering it, and discharging it to the outside atmosphere provides a safe work environment without significantly polluting the atmosphere. It does, however, represent considerable waste of energy in the form of heat invested in the air. This is because for every cubic foot of particulate-carrying air which is discharged to the outside atmosphere a corresponding amount of air must be drawn into the plant and heated to a level suitable for the working environment. In some circumstances, this can require raising the temperature of tens of thousands of cubic feet of air per minute by as much as 70.degree. F. As a result, valuable amounts of energy are used to heat the air which is retained in the factory for a comparatively short time before being exhausted to the outside atmosphere.
It is, therefore, an object of this invention to provide a method of ventilation for machinery which will minimize the amount of particulates in the vicinity of the workers, as well as the amount exhausted into the atmosphere; which removes particulate laded air from the air surrounding dust producing machinery; which removes particulates from the air; which returns a substantial portion of the treated air to the vicinity of the processing equipment so that the amount of air brought into the factory and heated to room temperature can be markedly reduced, thereby to provide vast savings in the amount of energy used for heat; and in which the method for conserving heat energy may be practiced without extensive modification to the existing equipment.
It is the ultimate object of this invention to conserve natural resources used to heat factory air and to reduce the amount of contaminants exhausted into the atmosphere.
Other objects and advantages of the invention will be apparent from the remaining portions of the specification.